Radiocommunication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also, to provide the capabilities needed to support next generation radiocommunication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radiocommunication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition toward an all IP-based network.
One example of such an evolving network structure can be seen in the evolution of wideband code division multiple access (WCDMA) systems. Specified by 3GPP TSG RAN, WCDMA systems have evolved from their initial role as a 3G mobile communication system through the addition of High Speed Downlink Packet Access (HSDPA) in Release 5 and, subsequently, Enhanced Uplink (EUL) in Release 6 (which are sometimes jointly referred to as High Speed Packet Access (HSPA)) to provide data bandwidths which support broadband mobile data applications. For example, downlink and uplink data rates of up to approximately 14 and 5.7 Mbit/s, respectively, may be supported in systems designed in accordance with Release 6 of the HSPA standards. Among other things, such data rate improvements are achieved through the use of techniques such as hybrid automatic retransmission request (HARQ) with soft combining, higher order modulation, scheduling and rate control.
Of particular interest for the present discussion associated with the uplink is the scheduling feature of HSPA systems. The EUL in Release 6 introduces a new enhanced dedicated channel (E-DCH) which supports uplink data transmissions from a user's equipment (UE). The EUL is non-orthogonal such that uplink transmissions from different UEs interfere with one another. Thus, the shared resource on the EUL is the amount of tolerable interference in a cell, i.e., the total received power at a NodeB. Accordingly, transmissions on the E-DCH are controlled by a scheduler, located in the NodeB, which controls when and at what data rate the UE is permitted to transmit data.
UEs operating in WCDMA systems, including those designed in accordance with the HSPA standards, typically operate in one of three states shown in FIG. 1 in order to balance power consumption against transmission delay/response time. Therein, state 2 represents a “sleep” mode wherein the UE only occasionally powers up its transceiver equipment to check for paging messages. In the random access (CELL_FACH) state 4, UEs are typically able to transmit small amounts of data as part of a random access (RACH) process which leads to a transition to the active (CELL_DCH) state 6, in which UEs transmit and receive data normally using the E-DCH and a High-Speed Downlink Shared Channel (HS-DSCH) channels, respectively.
In some areas, HSPA may become a replacement to asymmetric digital subscriber line (ADSL) service for connecting PCs to the Internet. This change in user behavior has a corresponding impact on traffic load and network characteristics. For example, PCs run a range of applications that communicate in the background without the need for end-user interaction. Among other things, such background traffic includes keep-alive messages, probes for software updates, and presence signaling. To efficiently support this type of traffic, the 3GPP has worked to enhance the CELL_FACH state 4 in Releases 7 and 8 of the WCDMA standards. More specifically, in Release 7, HSDPA has been activated for UEs operating in the CELL_FACH state 4. Thus, in the downlink, UEs monitor the HSDPA control channels to detect scheduling information for their own specific identities (H-RNTI) and are able to receive data more rapidly from the network while in the random access state.
In Release 8 of WCDMA, the uplink has also been improved by activating E-DCH for UEs operating in the CELL_FACH. Transmission begins by the UE ramping up power on the transmission of random preamble sequences (as is done in Rel-99 of WCDMA) to establish contact with a serving NodeB, i.e., until an acknowledge with resource allocation message (ACK) or a not acknowledged message (NACK), is received by the UE. After having detected the preamble, the Node-B which is associated with a serving cell assigns the UE to a common E-DCH configuration (managed by that Node-B). The UE may then start transmitting data on the common E-DCH with contention being resolved by means of UE identities in the E-DCH transmissions. By enabling the UE to use the E-DCH for uplink transmissions while in the CELL_FACH state 4, a UE can then be efficiently moved to the CELL_DCH state 6 for continuous transmission. This enhancement significantly improves user perception of performance compared with systems built in accordance with Release 6 of the WCDMA standards.
However, by enabling UEs in the CELL_FACH state 4 to transmit and receive at higher data rates, there also comes the corresponding challenge of dealing appropriately with their increased contributions to the interference situation, e.g., intercell interference. It should be noted that the intercell interference situation is potentially more severe in CELL_FACH state 4 than in CELL_DCH state 6 due to the lack of soft handover, i.e. lack of transmit power control commands from non-serving cells and relative scheduling grants from non-serving cells.